, another to mississippi republican senator roger wicker. both discovered, stopped and tested at a postal facility. >> the mail is screen and these tests were undertaken at remote sites to mitigate risks to the general population. >> reporter: both sent out of memphis. one quote from the letter, to see a wrong and not expose it is to become a silent partner to its continuance. another letter is under investigation. back here in d.c., even the tourists feel the added police presence at the capitol. >> you can feel it, walking around, after boston. things are just a little more tense. >> we ran into senator dianne feinstein just near this spot on the third floor of the senate russell building after the lockdown. no word of any arrests or injuries. >> reporter: packages and letters were all tested, all cleared. in washington, scott mcfarland, ktvu channel 2 news. >>> more details here on the poison itself. what makes it such a serious threat is there is no known antidote. one person was killed by ricin in 1978. >>> bay area elected officials ar